Radio receiving circuit



April 16, 1929. CLEMENT I 1,709,061

RADIO RECEIVING CIRCUI'L Filed Aug. 29, 1924 9 1 #1 6% I ,f a F I in" fi.

J mml hum/0r Z aw A7 flame/2f t tl Patented Apr. 16, 1929.

UNITED STATES PATENT OFFICE.

LEWIS M. CLEMENT, OF MOUNTAIN LAKES, NEW-JERSEY, ASSIGNOR 'I'O WESTERN ELECTRIC COMPANY, INGORPORATED, OF NEW YORK, N. Y., A CORPORATION OF new YORK.

RADIO CIRCUIT.

Application fiIeGAugust 29, 1924. Serial No. 734,858.

This invention relates to radio receiving circuits and more particularly to tuned radio frequency amplifiers.

One of the principal Objects of the inven 'tion is to prevent the production of sustained oscillations in a tuned radio frequency a1nplifier.

A feature of the invention is a vacuum tube amplifier in; which the coupling capacity of the tube is neutralized for all frequencies. y

A further object is to improve amplifiers of the type wherein the potential of the plate coil is not effective upon the grid coil to produce oscillations.

A feature oi the invention is a loop, receiver wherein the capacity of the loop to ground is not affected by the position of the loop.

Other objects of this invention Will be apparent to those skilled in'the art from the following specification and claims.

In a specific circuit embodying the inven tion, these objects are accomplished by providing a loop aerial tuned by a condenser and loosely coupled to a second tuned circuit by symmetrically placed condensers Which may be variable. The mid-points of the loop and the inductancecoil of the tuned circuit are grounded and connected to the cathode of a suitable space discharge device or tube which may function as a detector, amplifier, or in the case Where a local oscillator is used to produce an inaudibleintermediate trequcncy, as a con'ibini lglt device for the local and received oscillations. The grid of the tube is connected to one end oi the tuned circuit. A condenser connected from the anode of the tube to the end oi the tuned circuit opposite that connected to the grid serves to neutralize the tendency of the inherent feed-back efi ect ot the tube to produce oscillations. If the anode-grid be considered as one capacity and the neutralizing condenser as another capacity, then the loop circuit, the coupling condensers and the tuned circuit are symmetrically arranged with re spect to these capacities. Furthermore, the loose coupling of theloop circuit to the tuned circuit causes the loop circuit to be electrically remote from the space discharge de vice. i

The figure is a diagrammatic representa I tion at a circuit embodying this invention.

of tube 6 is connected to one terminal of coil 3. The filament of tube 6 is connected to the center portion of coil 3 from which point connection is also taken to the midpoint of loop 1 and to ground. The balancing condenser 8 is connected between the plate of the I tube 6 and the second terminal of coil 3.

In the operation of: this device, when incoming signals are being received, an oscillating current Will traverse coil 7. The coil 1 7 may or may. not have sufficient distributed capacity to act as a circuit resonant at operating frequencies, but in either case, os cillations which are induced in coil 7 Will produce a variable potential at the plate terminal of this coil. This potential will be applied to the grid connection of coil 3 through the capacity oi: tube 6 causiuu the tuned circuit consisting oi? coil 3 and condenser l to oscillate. By the use of candenser 8 connected to the second terminal of coil 3 and the plate of tube 6' any potential Which is applied to one end of coil 3 will be applied equally to the other end,

will result in the balancing; condenser 8 also preventing oscillations being induced in loop 1 by the potential of coil 7.

Where one side of the loop is grounded, as has Often-Jimes been the custonnthe capacity of the loop to ground Will be affected by the position at the locp with respect to the surrounding objects. For instance, when one side of the. loop isv in proximity to a body of metal, should the loop be rotated through .180", the effect will be similar to changing takeniromthe midpoint, the capacity of the tube can still be balanced by condenser 8 for a given frequency provided the proper ratio in capacity. of the condenser to capacity of turbed and oscillations transmitted. through the-tubeis ttound. -However,when.the. frequency is-clianged, thisbalance will be disthejtube from. coil- 7. It balance is obtained in. this manner. the midpointconnection. of theiloop would have to beshittcd'to a correspondingrpointl This unbalancesof the loop would cause. theposition ofthe loop to effect dits capacity, a? teatureiwhichthis invention particularly aims t0 tIV01Cl. It. will be seen that witlrthe connectionsas shown,a single.

balancing condenser can be used'to neutralize the capacityofthe tube on the. tuned secondaryfcircuit andlalso on the loop., At the same time the aerial effect of the. loop, that is, the

capacityof the loop to ground which would tend tobrOaden the tuning of a circuit isreducedt'o-a minimum.

It will be. seen from the foregoing. that there is-provided a1 circuit which is highly advantageous in that it is dircctionahhighly selective, easily tuned and-adjusted, and with only slight or no tendency to becomeself oscillatory. The principles of thefinvention a are applicable to circuits containing, a plurality of tubes followingjthe tube (3 and i'unctioning as detectors,amplifiers,etc., or to only aflsingle tube having, telephone receivers in itsjo'utput circuit. c Although this invention has been shown .and'descr-ibed asappliedi to a. particular circuit it should be understood that. the invention is of general application andis only limitedin accord ance with: the toll owing, claims.

lVhat is claimed is: i i

1. Aradio receiver comprising a space discharge device, including, a cathode, anode and control'electrode, a'tuned circuit containing a loop wave. 1ntercepter,. a second tunedv circuit including an inductance, ca-

pacitivel'y coupled to. loop by. two condensers, and connected to electrodes of said device, said condensers being syn'unetrically located with respect to said tuned circuits, a condenser of approximately the same capacity as said discharge device connected between the anode of said device and the second tuned-circuit for preventing spurious oscillations in the two tuned circuits, and a common ground'conncction to said cathode and to the respective mid-points oi said intcrcepter and said inductance, whereby said circuits are maintained balanced during the rotation of said intercepter.

2. A radio receiving system comprising a tuned loop circuitand a second tuned circuit including a coil coupled to the tuned loop circuit by capacity elements symmetrically located with respect to said circuits, :1 device having an inherent feed-back effect due to inherent capacity therein connected across a portion of said tuned circuit, a single capacity connected between the output circuit of said device and an electrically opposed portion ofsaidtuned circuit, and a coalition ground connectionto the midpoint of said loop and the midpoint of the coil in said tuned circuit. 3. A. loop antenna tuned by a condenser and having, its midpoint grounded and connected to the cathode of a vacuum tube relay, a tuned circuit having its midpoint grounded and connected to said cathode, variable 'capacities symmetrically related to the tuned loop and-the tuned circuit for coupling the ends ofsaidloop antenna directly to the ends of. said circuit,.a connection from an end of said circuit to aoontrol electrode of said relay,. and a condenser connected from the anode of said relay to the other end of said circuit for preventing spurious oscillations in the tuned loop and-the tuned circuit.

4. In a radio receiving circuit, a tuned loop circuit,.a vacnumtube havinginput and outputcircuits, :1 second tuned circuit. includingya coil, capacity. elements for connecting-the ends of said loop to the ends of said'coihineans connecting the input circuit of said tube to one end and the electrical center of said coil, asmall condenser having approximately the same capacity as the capacity of saidtube connected to the anode of the tube and. the second terminal of the coil, a tuned-circuit connected to the output circuit of said tube, and means connecting the electricalcenter of said coil and the center of said loop to ground.

In wit-ncsswhcreof, I hereunto subscribe my name this 26th day of August, A. D. 1924.

LEWIS M; CLEMENT. 

